The Edge - Quarter 4, 2008 - (Page 18)

HOT WATER CHEMISTRY | by Joe Sweazy Treating Hot Water? Don’t Mistake It for a Pool Big and small, hot and cool. What’s the difference? Can’t you just fill them with water, test them and treat them the same? Unfortunately, no. Swimming pools and spas must be cared for in different ways. Spas and hot tubs operate at a higher temperature, and they are much smaller as well. These two factors change everything. That is why there are separate ANSI/APSP standards (Association of Pool & Spa Professionals) in the U.S. for spas and pools. The two big differences—higher temperature and smaller volume—cause a number of other changes that need to be taken into consideration. Higher temperature will cause: faster chemical reactions; faster evaporation rate; increased scale formation; more organic waste in the water; and accelerated bacteria growth. Smaller water volume will cause: heavier bather load; exact chemical dosages needed; higher fi ltration (turnover) rate; faster depletion of sanitizer residual; and more abrupt changes in pH. aeration. As the water evaporates, the spa owner adds makeup (fi ll) water to refresh the system. Any water that evaporates is pure water; what gets left behind is everything else— the stuff that we call TDS (total dissolved solids). Any makeup water will also contain minerals, salts and other dissolved substances that increase the total dissolved solids in the spa. Therefore, each time fresh water is added, the TDS level is increased. High levels of TDS decrease the effectiveness of some chemicals and may cause cloudy and/or foamy water. Higher temperatures in spa water will cause most chemicals to dissolve faster than at lower temperatures, except calcium carbonate. This form of hardness works in the opposite way: it actually is more insoluble in hot water. Therefore, calcium carbonate scale is more likely to occur in hot spa water. Additionally, high levels of calcium hardness can cause or contribute to cloudy water. The hot water in spas also makes people sweat. The average bather sweats a pint (about half a liter) in just 20 minutes. Plus, the power jets in a spa can scrub off dirt and dead skin very quickly. All of this means that the filter and chemical sanitizer in a spa must process a high percentage of waste. Consequently, paying close attention to the sanitizer level is critical in a spa. If not cared for properly, a spa makes a perfect incubator for bacteria. Hot water promotes the growth of most types of bacteria. Susceptible bathers can acquire serious illnesses if water is not chemically balanced. HIGHER WATER TEMPERATURES Pools usually operate between 76 degrees and 86 degrees F (25 degrees—30 degrees C), while spas fall in a range between 96 degrees and 104 degrees F (36 degrees—40 degrees C). This difference in temperature changes the water chemistry in important ways. Chemical reactions take place much faster in spas than in pools. For every 18 degrees F (10 degrees C) increase, the typical chemical reactions proceed twice as fast. For instance, a spa at 102 degrees F allows chemical reactions to happen in half the time of a pool at 84 degrees F. Any chemical adjustments occur more quickly. The water comes to equilibrium sooner and water treatment can be completed in a shorter period of time. The water in a spa also evaporates at a higher rate due to higher water temperature, rapid water circulation and 18 www.nespapool.org SMALLER WATER VOLUME Clearly, spas have a much smaller volume of water than pools. This obvious difference also affects the water chemistry. Spas experience a much heavier bather load because they are so much smaller. While two people in a spa might feel http://www.nespapool.org

Table of Contents Feed for the Digital Edition of The Edge - Quarter 4, 2008

The Edge - Quarter 4, 2008 Contents The President’s Message New Pool/Spa Federal Safety Act Worried About the 2009 Market? Treating Hot Water? Project Focus The 411 on UV Disinfection for Pools and Spas The Advantages of Seeding Aggregate Surfaces Pool and Spa Industry Wins Gold Choosing a Retirement Plan To Get Best Coverage at Lowest Cost - Shop Now Index of Advertisers

The Edge - Quarter 4, 2008

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